This application claims priority from Japanese Patent Application Serial No. 2000-314678 filed Oct. 16, 2000.
1. Field of the Invention
The present invention relates to an iron golf club (hereinafter, simply referred to as a xe2x80x9ccavity ironxe2x80x9d) having a cavity portion on the rear surface side of the face portion and a golf club set, and more specifically, to a cavity iron golf club provided on a surface of a sole portion defining the cavity portion with a groove for adjusting a thickness of the face portion while increasing an effective face length and a golf club set having such a golf club.
2. Description of the Background Art
Conventionally, a cavity iron golf club is known in which a sole portion is formed in an undercut-shape in order to achieve weight reduction and to position the centroid position toward the rear side of the face, i.e. deepening the centroid. This type of iron golf club head is disclosed, for instance, in Japanese Utility Model Publication No. 5-27951.
FIG. 23 is a cross sectional view of an iron golf club head disclosed in Japanese Utility Model Publication No. 5-27951.
As shown in FIG. 23, a head portion 1 includes a cavity portion 2, a face portion 3 having a ball hitting surface, and a sole portion 4. An undercut surface 5 is formed by slanting the surface of sole portion 4 defining cavity portion 2. In this manner, by forming undercut surface 5, the centroid depth can be deepened while achieving weight reduction of head portion 1.
In the above document, however, no mention is made of the thickness of face portion 3, and the thickness of face portion 3 is uniform as shown in FIG. 23.
The cavity iron of the type shown in FIG. 23 has excellent directivity of the hit ball, but also has the problem that improvement in carry cannot be achieved.
In addition, since the thickness of face portion 3 is uniform, the cavity iron of FIG. 23 had the problem of significant reduction in the carry in the case of an offset strike where a golf ball is struck at a location other than the sweet spot.
The present invention is made to solve the above problems. The object of the present invention is to deepen the centroid depth of a golf club head, to increase the moment of inertia in the toe-heel direction, and to improve the directivity of the hit ball while preventing too great a reduction in the carry upon an offset strike in a cavity iron golf club.
An iron golf club according to the present invention is provided with a head portion having a cavity portion, a face portion, and a sole portion, and a groove extending along the face portion is provided on a surface on the cavity portion side of the sole portion, and a thickness of a ball hitting portion in the face portion is made greater than a thickness of a top edge side portion of the face portion located between the ball hitting portion and a top edge portion and at least as thick as a thickness of a sole side portion of the face portion that is located between the ball hitting portion and the sole portion and that extends along the groove.
By providing the groove on the surface on the cavity portion side of the sole portion as described above, an effective face length can be lengthened. Here, the effective face length refers to a length of a portion of the face portion that can flex when hitting a ball, and is a length in the direction from the sole portion toward the top edge portion. By lengthening the effective face length, the face portion becomes more flexible, and thus, the restitution property of the face portion can be improved. Moreover, by making the thickness of the ball hitting portion in the face portion greater than the thickness of the top edge side portion and the thickness of the sole side portion of the face portion, the face portion becomes even more flexible, and the restitution property of the face portion can be effectively improved. Furthermore, by providing the groove, the centroid depth of the golf club head becomes deeper, so that the moment of inertia can be increased and the directivity of the hit ball can be improved.
The thickness of the ball hitting portion is made greater than a thickness of a toe side portion of the face portion located between a toe portion of the head portion and the ball hitting portion and greater than a thickness of a heel side portion of the face portion located between a heel portion of the head portion and the ball hitting portion. In this case, also, the face portion can be made more flexible and the restitution property of the face portion can be improved. In addition, formation by forging is preferable in order to make the thickness thin while maintaining strength in the toe side portion and the heel side portion.
The toe side portion includes a first region located on the top edge portion side and a second region located on the sole portion side, and the heel side portion includes a third region located on the top edge portion side and a fourth region located on the sole portion side. In this case, a thickness of the first region is preferably made smaller than a thickness of the second region, and a thickness of the third region is preferably made smaller than a thickness of the fourth region. Thus, the face portion can be made even more flexible and the restitution property of the face portion can be improved.
Preferably, the height of a base surface of the groove from a base surface of the sole portion is made lower on the heel portion side than on the toe portion side.
Normally, the height of the face of the iron golf club head is made higher on the toe portion side and lower on the heel portion side. By making the height of the base surface of the groove from the base surface of the sole portion lower on the heel portion side than on the toe portion side, the effective face length can be lengthened on the heel portion side as well. Consequently, the effective face lengths can be made equal on the toe portion side and the heel portion side so that the restitution property can be improved even when a ball is struck on the toe portion side or on the heel portion side in the case of the offset strike.
The sole portion includes a projected wall portion that defines one of side walls of the groove and that rises along the face portion toward the top edge portion. This projected wall portion has a trapezoid-like shape, for instance.
As described above, by providing the projected wall portion behind the face portion, the centroid depth can be deepened and the directivity of the hit ball can be improved.
A through hole is provided in the sole portion such that it reaches the cavity portion from the base surface of the sole portion, and the groove may be provided by attaching a blocking member that closes an end portion on the base surface side of the sole portion in the through hole. Thus, a deep groove can be formed in the sole portion along the face portion, and the effective face length can be lengthened.
The specific gravity of a material composing the blocking member is preferably made greater than the specific gravity of a material composing a head portion body. Thus, the centroid position of the golf club head can be lowered.
A back side portion located behind the face portion in the head portion may be formed by a back part which is a separate member from the head portion body. In this case, by attaching the back part to the head portion body, the groove is provided between the head portion body and the back part. In this manner, by making the back side portion of the head portion a separate member from the head portion body, a deep groove can be formed in the sole portion along the face portion and the effective face length can be lengthened, as in the case where the through hole is provided as described above.
The specific gravity of a material composing the back part is preferably made greater than the specific gravity of a material composing the head portion body. Thus, the centroid depth of the golf club head can be made deeper, while lowering the centroid position.
In one aspect, a golf club set according to the present invention includes a long iron golf club (for instance, No. 1 to No. 4 iron golf clubs), a middle iron golf club (for instance, No. 5 to No. 7 iron golf clubs), and a short iron golf club (for instance, No. 8 iron golf club to a sand wedge). Each of the long iron golf club, the middle iron golf club, and the short iron golf club is provided with a head portion having a cavity portion, a face portion, and a sole portion, and is provided with a groove extending along the face portion on a surface on the cavity portion side of the sole portion. The depth of the groove in a center portion of the face portion of the long iron golf club is greater than the depth of the groove in a center portion of the face portion of the middle iron golf club, and the depth of the groove in the center portion of the face portion of the middle iron golf club is greater than the depth of the groove in a center portion of the face portion of the short iron golf club.
As described above, by gradually making the depth of the groove provided in the sole portion deeper from a short iron golf club toward a long iron golf club, greater increase in the effective face length and thus higher restitution property can be achieved toward the long iron golf club of which long carry is demanded, and a golf club set whose emphasis is on improved carry can be provided.
In another aspect of the golf club set according to the present invention, a groove extending along the face portion is provided on a surface on the cavity portion side of the sole portion of each of the long iron golf club and the middle iron golf club, and the depth of the groove in a center portion of the face portion of the long iron golf club is made greater than the depth of the groove in a center portion of the face portion of the middle iron golf club, while the groove extending along the face portion is not provided on a surface on the cavity portion side of the sole portion of the short iron golf club. In this case, also, the same effects as those obtained in the above-described one aspect can be achieved.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.